How to Make It
Put the onions in a heatproof medium bowl. In a medium saucepan, combine the vinegar with the sugar, chiles, salt and 1 1/2 cups of water and bring to a simmer over moderate heat, stirring, until the sugar dissolves, about 2 minutes. Pour the brine over the onions, cover and let stand for 1 hour. Discard the chiles.
In a medium saucepan, combine the lentils with the garlic, salt and chile and cover with 2 inches of water. Bring to a simmer and cook over moderate heat until the lentils are tender, about 15 minutes. Drain the lentils; discard the chile and garlic. Transfer the lentils to a bowl. Add 2 tablespoons of the olive oil, season with salt and pepper and toss to coat.
In a medium bowl, mash the avocados with the lemon juice and season with salt.
Light a grill or preheat a grill pan and brush with canola oil. Rub the salmon with the remaining 2 tablespoons of olive oil and season with salt and pepper. Grill over moderate heat, turning once, until just opaque throughout, 6 to 8 minutes per side; transfer to a platter.
Serve the salmon and lentils with the mashed avocado, pickled red onions, warm corn tortillas and hot sauce.